Re: [Emc-users] Home made spindle encoder question.
Jeff Epler wrote: Why is it important that the signals be close to 90 degrees out of phase? Here's why: imagine they're some smaller amount (e.g., 45 degrees). That means that there's a smaller time for at least one of the 4 states of the quadrature progression at any given speed. In the 45 degree case, it makes the maximum accurate count rate only half of what it could optimally be for a perfect 90 degree phase differences. Jeff While others have answered the question already I would like to add that I was able to see a demo of magnetic rotary and linear encoders http://www.austriamicrosystems.com/eng/Products/Magnetic-Encoders/Rotary-Encoders at Embedded Systems Conference in San Jose CA yesterday. Very impressive resolutions can be achieved, 25 um with speeds up to 20m/s. I know this has been discussed before but seeing is believing. I hope that prices come down eventually. -- Rafael -- ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Home made spindle encoder question.
On Fri, 03 Apr 2009 19:52:21 -0400, you wrote: Yes. They can be any distance apart as long as the distance adds a half a slot. And I believe I would adjust that by using a dual trace scope to get it as close to 90 degrees out of time as I could, opto stuff works by ir diodes and measuring it physically could be a long way off of 90 degrees just from tolerance in the opto-interrupters. No problem with the opto's, they are buffered OPB916B's - rise/fall time of just 50nS with a nice clean signal. I will be using a scope to set them up, I'll make the bracket so the opto's can be adjusted more than a slot and a space in relation to each other. Motor reverse is going to need some sort of a servo lashup. I'm doing the spindle motor in my micromill with a repaired original driver, removed from the mill head and installed alongside a PMDX-106 in a 3.5x4.5x7 plastic box, with 2 dpdt PB relays boosting the teeny ones on the PMDX-106, so I have complete speed and direction control right from emc. But I haven't servo'd it yet, mainly because of the difficulty in attaching an encoder disk like yours to the spindle. Reversing works now, all I need it to do is be predictable where it stops on commanding a stop/reverse. If anyone comes up with an idea of how that might be done internally to the micromills now nearly empty head houseing, without drowning the opto's in flying grease from all those plastic gears, I'm all ears. Get rid if the gears and use timing belts, no grease then ;) Steve Blackmore -- -- ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
[Emc-users] Home made spindle encoder question.
My lathe has a 100 slotted disc on the spindle, with one opto switch fitted so far, the slot for that is longer than the others and gets me one pulse per rev. It works fine to 3500 rpm as a rev counter. I want to add two more opto's to get me an A and B channel to enable spindle control for threading under EMC. Motor reverse is essential too. Are there any specifics as to the positioning of the opto's in relation to each other? Do they need to be only a few slots apart, or more? I think that the A B need to be 1/2 slot out of sync - is that correct? Thanks Steve Blackmore -- -- ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Home made spindle encoder question.
On Fri, 3 Apr 2009, Steve Blackmore wrote: Date: Fri, 03 Apr 2009 21:23:41 +0100 From: Steve Blackmore st...@pilotltd.net To: emc-users@lists.sourceforge.net Subject: [Emc-users] Home made spindle encoder question. My lathe has a 100 slotted disc on the spindle, with one opto switch fitted so far, the slot for that is longer than the others and gets me one pulse per rev. It works fine to 3500 rpm as a rev counter. I want to add two more opto's to get me an A and B channel to enable spindle control for threading under EMC. Motor reverse is essential too. Are there any specifics as to the positioning of the opto's in relation to each other? Do they need to be only a few slots apart, or more? I think that the A B need to be 1/2 slot out of sync - is that correct? Yes, 1/2 slot (90 degrees) OPTOSs can be N+1/2 slots apart, but on same slot is probably better for minimizing quadrature distortion (and possible miscounts) due to errors in your wheel Thanks Steve Blackmore -- -- ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users Peter Wallace Mesa Electronics (\__/) (='.'=) This is Bunny. Copy and paste bunny into your ()_() signature to help him gain world domination. -- ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Home made spindle encoder question.
On Fri, 2009-04-03 at 21:23 +0100, Steve Blackmore wrote: My lathe has a 100 slotted disc on the spindle, with one opto switch fitted so far, the slot for that is longer than the others and gets me one pulse per rev. It works fine to 3500 rpm as a rev counter. I want to add two more opto's to get me an A and B channel to enable spindle control for threading under EMC. Motor reverse is essential too. Are there any specifics as to the positioning of the opto's in relation to each other? Do they need to be only a few slots apart, or more? I think that the A B need to be 1/2 slot out of sync - is that correct? Thanks Steve Blackmore Just in case, I've seen some spindle disks using holes, the slots and fingers should be the same width so that you get a 50% duty cycle. A ___|^^^|___|^^^|___ B _|^^^|___|^^^|___|^ Another thing comes to mind, as an edge goes by the light has an analog transition that is squared up by the receiver at some on/off and off/on point. It seems that for DIY encoders you would want to be able to adjust that on and off trip point, so that you could get a 50% duty cycle. Although it may not really matter in practice. - Kirk http://www.wallacecompany.com/machine_shop/ -- ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Home made spindle encoder question.
Steve Blackmore wrote: My lathe has a 100 slotted disc on the spindle, with one opto switch fitted so far, the slot for that is longer than the others and gets me one pulse per rev. It works fine to 3500 rpm as a rev counter. I want to add two more opto's to get me an A and B channel to enable spindle control for threading under EMC. Motor reverse is essential too. Are there any specifics as to the positioning of the opto's in relation to each other? Do they need to be only a few slots apart, or more? I think that the A B need to be 1/2 slot out of sync - is that correct? They need to have a 90 degree phase relationship - that's the definition of quadrature. So, just as one sensor is dead center in the slot, the other should be right on the edge. The actual spacing in number of slots between the sensors is not important. But, in any case, they should be some full slot multiple, plus 1/4 of a slot, apart. Jon -- ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Home made spindle encoder question.
Why is it important that the signals be close to 90 degrees out of phase? Here's why: imagine they're some smaller amount (e.g., 45 degrees). That means that there's a smaller time for at least one of the 4 states of the quadrature progression at any given speed. In the 45 degree case, it makes the maximum accurate count rate only half of what it could optimally be for a perfect 90 degree phase differences. Jeff -- ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
